1) Astronomical instrument 
An Eidouranion is a kind of orrery that combined mechanical movement with a method of back projection. Its invention is attributed to Adam Walker who in the 1780s built one measuring 27 feet in diameter. He used it to accompany his lectures on astronomy. It is an ancestor of planetarium projectors. It is known that Adam Walker held lectures featur...
eidouranion A contrivance for illustrating the motions of the heavenly bodies.